This invention relates to a prosthetic joint, and more particularly to a prosthetic joint for total knee replacement. The prosthetic joint is adapted to be implanted in the body of a subject human or animal.
Heretofore, prosthetic joints have been used to replace defective natural joints in humans and animals when such joints have become diseased or injured through accident. However, prior art prosthetic members have not been wholly satisfactory for knee implantation because they do not provide for the complexity involved when flexing the tibia relative to the femur. Furthermore, the prior art prosthetic joints do not provide for replacement of wear surfaces without completely removing the implanted unit. Some prior art prosthetic joints tend to become inoperative because of wear. This may reduce their ability to perform the complicated movements inherent in natural knee joints. While suitable prosthetic members have been devised utilizing simple ball joint construction, it has been found that a surface-to-surface contact of the external parts of the joint provide better movement. This surface-to-surface external contact of the spaced-apart prosthetic members cause wear of the surfaces and in time replacement is required.
Accordingly, it is an object of this invention to provide a new and improved joint prosthesis for total knee replacement which enables replacement of worn parts without necessitating the complete removal of the implanted units.
Briefly, the femoral member of the joint prosthesis includes two locking pins designed to prevent the ball and socket components from subluxating after insertion. The tibial member is provided with a boss to receive a recess in a plateau which forms a bearing surface between the femoral and tibial members. The plateau structure allows a surgeon to replace it in the event of significant wearing of the bearing material. Also the ball and socket unit can be replaced by the construction of the present invention.
Instead of being pressed over a narrow pin, which makes replacement very difficult, the plateau slides over a metal boss formed on the upper surface of the tibial member and is held in place by a ball stud anchor screw. The ball stud is inserted into a blind hole and held in place by the ball stud anchor screw which extends transversely therethrough. Therefore, threading of the ball stud into the tibial member is unnecessary and thereby facilitates removal of the components.
In order to avoid the possibility of the anchor screw moving or backing out of the boss member, cruciate slots have been cut into the posterior aspect of the anchor screw to provide diametrically opposed locking tab members at the end thereof. The locking tab members are flared out to conform to the shape of a chamfer on the posterior aspect of the metal boss of the tibial component. If replacement of the ball and/or plateau is necessary, the anchor screw can be easily removed with a socket head hexagon wrench. During removal of the ball and/or plateau, the femoral and tibial components inserted into the corresponding bone members remain intact.
Many of the obvious features and advantages of this invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements and components.